Summary: There is limited data on the nature of the immune response that leads to protection from Anthrax. Antibodies to protective antigen (PA), a critical component of anthrax lethal and oedema toxins, have been shown to correlate with protection. However, studies suggest that other factors may play a role and little has been done to explore the role of T-lymphocytes in protection from and/or exacerbation of Anthrax. This lack of information regarding the localization and phenotype of T-lymphocyte responses to Anthrax toxins prevents design of appropriate therapeutics and improved vaccines. Development of immune based therapies and acellular Anthrax vaccines will require an understanding of Anthrax toxin antigen presentation and the response of T-lymphocytes to toxin antigen. We plan to address these questions using recombinant Anthrax toxins. These molecules will allow evaluation of toxin trafficking and antigen presentation of toxin. After generating data on antigen presentation with in vitro experiments using cell lines, the same recombinant toxins can be used for in vivo experiments. Histochemical evaluation of tissues from these animals will facilitate visualization of in vivo anthrax toxin localization and the subsequent immune responses. Visualizing the sub-cellular localization of Anthrax toxins and the in vivo immune response to these toxins can facilitate the design of assays to evaluate protein therapeutic effects on anthrax toxin. This information is important for development of safe and effective therapeutics and toxin subunit vaccines.